Kasu Mohaimin, Shires Karen
Division of Forensic Pathology, University of Cape Town, South Africa.
Division of Haematology, University of Cape Town, South Africa; National Health Laboratory Services/Groote Schuur Hospital, Haematology, Cape Town, South Africa.
Leg Med (Tokyo). 2015 Jul;17(4):232-8. doi: 10.1016/j.legalmed.2015.01.004. Epub 2015 Feb 7.
The production of full DNA profiles from biological evidence found in soil has a high failure rate due largely to the inhibitory substance humic acid (HA). Abundant in various natural soils, HA co-extracts with DNA during extraction and inhibits DNA profiling by binding to the molecular components of the genotyping assay. To successfully utilize traces of soil contaminated evidence, such as that found at many murder and rape crime scenes in South Africa, a reliable HA removal extraction system would often be selected based on previous validation studies. However, for many standard forensic DNA extraction systems, peer-reviewed publications detailing the efficacy on soil evidence is either lacking or is incomplete. Consequently, these sample types are often not collected or fail to yield suitable DNA material due to the use of unsuitable methodology. The aim of this study was to validate the common forensic DNA collection and extraction systems used in South Africa, namely DNA IQ, FTA elute and Nucleosave for processing blood and saliva contaminated with HA. A forensic appropriate volume of biological evidence was spiked with HA (0, 0.5, 1.5 and 2.5 mg/ml) and processed through each extraction protocol for the evaluation of HA removal using QPCR and STR-genotyping. The DNA IQ magnetic bead system effectively removed HA from highly contaminated blood and saliva, and generated consistently acceptable STR profiles from both artificially spiked samples and crude soil samples. This system is highly recommended for use on soil-contaminated evidence over the cellulose card-based systems currently being preferentially used for DNA sample collection.
从土壤中发现的生物证据生成完整的DNA图谱失败率很高，这主要归因于抑制性物质腐殖酸（HA）。HA在各种天然土壤中含量丰富，在提取过程中会与DNA共同提取，并通过与基因分型检测的分子成分结合来抑制DNA图谱分析。为了成功利用受土壤污染的微量证据，比如在南非许多谋杀和强奸犯罪现场发现的证据，通常会根据之前的验证研究选择可靠的HA去除提取系统。然而，对于许多标准的法医DNA提取系统，详细说明其对土壤证据有效性的同行评审出版物要么缺乏，要么不完整。因此，由于使用了不合适的方法，这些样本类型往往没有被采集，或者未能产生合适的DNA材料。本研究的目的是验证南非常用的法医DNA采集和提取系统，即用于处理被HA污染的血液和唾液的DNA IQ、FTA洗脱法和Nucleosave。将适量的法医生物证据加入HA（0、0.5、1.5和2.5毫克/毫升），并通过每个提取方案进行处理，以使用定量聚合酶链反应（QPCR）和短串联重复序列（STR）基因分型评估HA的去除情况。DNA IQ磁珠系统有效地从高度污染的血液和唾液中去除了HA，并从人工添加样本和原始土壤样本中一致地生成了可接受的STR图谱。与目前优先用于DNA样本采集的基于纤维素卡的系统相比，强烈推荐该系统用于处理受土壤污染的证据。
